combination, but I doubt that would be very efficient
slightly less accurate. Or maybe someone knows of a
If your resistance range is not too large, and the signals you will impress across it is small enough, a quad MOSFET array can be made to perform that function with an op-amp controlling it.
What input and output range to you need, over what frequency range, with what distortion?
Another approach is to use a multiplier IC, hooked up as a divider, with voltage input and current fed back from the output to the input. But again, the required specs are necessary to proceed.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
combination, but I doubt that would be very efficient
slightly less accurate. Or maybe someone knows of a
... [MOSFET array cut as unlikely to be suitable.]
...
There will be accuracy and current capacity issues with the low end of that range. What a designer will need to know, (at least), is: What currents or voltages will be applied to the resistance?
something that isn't all that precise anyway.
That will certainly help.
anything within that.
Right now, your requirement appears to be:
Accept an input voltage, 'Vx', ranging between 0 V and 9 V, on one port, consisting of pins VxIn and VxRef.
Provide a "resistance", 'Ro', on another port, consisting of pins RoA and RoB.
If current is passed thru Ro, the voltage across it should be Vx * 2500/9, within some unknown tolerance. There is no presently known limit on what that current might be.
If a voltage is applied across Ro, the current passing thru it should be 9/(2500 * Vx), within some unknown tolerance. There is no presently known limit on what that voltage might be.
The accuracy implied by items 3 and 4 applies only over the frequency range 0.2 Hz to 20 Hz. Outside that range, any voltage or current result is acceptable.
The connection, if any, between the Vx port and Ro port, is unspecified. They might be required to be isolated from each other for an unbounded voltage difference. Or it may be fine for either RoA or RoB to be connected to VxRef.
I state the above to clarify what is missing. For any of the unknown bounds and limits, smaller will be easier and if it can be unipolar rather than having to be bipolar, the design may be simplified. Not having to isolate the ports will greatly simplify the problem.
What sort of circuit is going to use the synthesized resistance? Can it accept a voltage or current instead? There may be an easier way to solve the real problem than synthesizing a resistance.
You're welcome.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
If I have a source of variable voltage ( a sweep generator for example), is there any way to create a source of varying resistance in proportion to the voltage?
About the only way I can think of off the top of my head is a light/LDR combination, but I doubt that would be very efficient or accurate.
Anyone have any better ideas? Preferably simpler ones, even if it is slightly less accurate. Or maybe someone knows of a resistance sweep generator...
If you want to take digital potentiometer for this task, it should be possible, but it will require a SPI or similar control signal, not a voltage input. If you modify the circuit, you might come to a solution with a multiplyer, but this is not a trivial case either. You can use the LDR/LED approach, but the lowest resistance will not be 0, but maybe 400 to 1k, so you get less range into the clean sound, where the circuit acts merely as a follower. It can be tried out easily, there are even combinations in a 8DIP readily available, I do not remember the part numbers, but google should help. Some manufacturers make motor pots, I saw some surplus ones go for only 6 bucks, but only 10k, not 2k5. (k is not in capital letters, BTW).
The circuit looks faulty as you have drawn it. Look at the signal path from the collector, through a 1uF, to the wiper of R1, through a 1uF, to the output. That is a very low impedance path, practically a shortcircuit for AC signals. The collector signal will be at the output in full force, no matter how R1 is set.
Now you want to mix into that signal the opposite phase from the emitter, by using R1, and what effect do you want to achieve by that?
I think the signal from the emitter will hardly be stronger that the collector signal, so the result will be an attenuation of the signal, which could be achieved a lot simpler, if that is what you want.
Maybe you have made a mistake in the drawing, so the connection between the collector output cap to the wiper of R1 should be erased?
Then we will at least get something meaningful, a circuit which can move between positive phase, through nothing, to negative phase, by moving the wiper of R1.
If we replace R1 with a pair of FET transistors we can voltage control how much positive or negative phase goes to the output. Or by using analog gates, type 4066 series, the same effect can be achieved.
But basically I think the whole project seems badly concieved and designed. What you really need is to start over from the beginning, make it clear what you want to achieve, and ask for help to design a circuit to do that.
simple phaser. Apparently it works by using the fact
something). The varying resistance has been labelled R1.
I concur with Roger on the misconnection between the top end of the pot and its wiper.
difference to anything.
Sorry, but I cannot understand what you mean by that. Are you saying you want the resistance versus control voltage function to be a sinusoid? Or that you intend to use sinusoids as the control voltage?
power supply.
That pretty much resolves the isolation issue. The control voltage can be assumed to share the same ground with your "phaser".
isolate resistance, or the difference between unipolar
(changing DC?) and that bipolar means otherwise (AC?).
confused.
You've roughly got the bipolar/unipolar distinction, except bipolar means can have either of two signs and unipolar means can have only one sign or be zero. A bipolar signal could have DC content or not, and it is meaningful to speak of the AC content of a unipolar signal. The AC/DC concept and the unipolar/bipolar concept are not the same.
if anyone has any suggestions, that would be great.
There are many ways to do that. Digitally synthesized sine generators are pretty cheap these days.
dealt with this type of circuit before, so I can't
Yes. But I am not inclined to help go down the synthesized resistance route. (I concur with Roger on that as well.)
It would be easier to build a voltage controlled "phaser" than to synthesize a voltage controlled resistance to put into that circuit you drew.
For example, by differencing the output of two multipliers, one fed with (Vmax - Vcontrol) and the other fed with (Vcontrol), (where Vmax is the fullscale multiplier input), you would get the effect you are after. You can get a good multiplier in an 8 pin package.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
There is a nifty way to do this with plain old 4016 analog switches. You use the input voltage to control the duty cycle of a high-frequency oscillator. The 4016 (or 4066, etc) plus some minimum resistance is used as the variable resistor. The effective resistance (amount of current that flows for any voltage) is then proportional to the duty cycle. The beauty of this is that once you build up the PWM control circuit, all stages can be made to track very closely, and adding another stage only involves adding one more 4016 section.
Don Lancaster discussed this in his CMOS Cookbook. I have used it (many years ago) to create a phaser effect with multiple stages to give more notches. All you have to worry about is getting the PWM clock above the audio range.
Best regards,
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
something). The varying resistance has been labelled R1.
difference to anything.
power supply.
isolate resistance, or the difference between
below 0V (changing DC?) and that bipolar means
DC, or am I getting confused.
so if anyone has any suggestions, that would be
dealt with this type of circuit before, so I can't
(Sheepishly), the same function can be accomplished with a single 4-quadrant multiplier. One input is the audio to be subjected to "phaser" manipulation, the other input is biased to be +/- fullscale at the extremes of the control input range, and the audio output is the multiplier output. With suitable biasing, it could all be done with a single supply and an 8-pin multiplier such as the AD835. See
formatting link
You're welcome.
--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.
I have decided in the end that it is getting too complex. I'll still probably tinker around with it, and try out your suggestion of the multiplier. I'll probably try and find complete circuits of DIY guitar FX pedals, at least until I gain a bit more knowledge on some of this stuff.
I have learnt some things though, and learning about electronics is one of the main reasons I try to make guitar effects pedals.
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